This reusable vehicles characteristics will enable observation of atmospheric trace components, aerosol, and fine particles as well as continuous sampling of atmosphere and fine particles, allowing us to conduct frequent, high-precision measurement of spatial and temporal changes in the earths atmospheric environment at a number of places. Thus, the early detection of minimal changes in our planets environment is expected to bring innovative results to global environmental monitoring. In addition, for research using a microgravity environment such as life science and materials science, the reusable rockets should bring continuous and repeatable experimental opportunities, easy recovery of experimental instruments, and provide an excellent environment for microgravity experiments. Such qualitative and quantitative innovation of the experimental environment will radically stimulate research activities and their results. Moreover, by repeating launches, we can gain broader recognition from the world. By drastically lowering the bar for participation in space experiments, it is expected that many rocket users will appear with new rocket-born research proposals. The current sounding rockets have already brought many successful results. Frequent operation of our reusable vehicle must have a dramatic effect on research using the sounding rockets.
Technological demonstration of reusable sounding vehicles
Is it easy to develop a reusable sounding vehicle? The reusable rocket will have a system that is quite different from a conventional expendable rocket. The reusable rocket (i) repeats flight operation; (ii) makes re-entry and lands; and (iii) returns safely even after failure. To build reusable vehicle, we must solve technical problems that do not occur with conventional rockets. We are grappling with technological demonstration necessary for the realization of reusable rocket.
(i) Repeat flight operation
Our challenge includes reusing the engine one hundred times.EConsidering thrust performance and future prospects, we plan to use a liquid oxygen and hydrogen propellant engine for our rocket. In every flight, the engine must endure the harsh conditions created by the high temperature and pressure under which hydrogen and oxygen are mixed to combust. In Kakuda Space Center we built a reusable engine and conducted technological demonstrations for its repeated use. The engine design puts a higher priority on reusability and thrust control for landing than engine performance itself. The design also differs from conventional engines in its labor/cost-saving ideas such as easy maintenance and parts replacement.
(ii) Return flight and landing
While expendable rockets could ignore the return to earth, a reusable vehicle needs new ideas such as: what manner of flight and what fuselage shape will enable the return flight? We are now designing the fuselage system, conducting wind-tunnel tests to determine its shape, and preparing for a flight demonstration by small experimental vehicle. We are also considering vertical landings made by restarting the engine before landing. Our plan is a system that both lifts off and lands vertically. As part of this technology, we researched liquid-fuel behavior and pressure changes in the tanks during the return flight, and are designing devices needed to restart the engine to be installed inside the tanks.
(iii) Returning safely even when failure occurrence
If a conventional rocket has an engine failure during its flight, the flight is abandoned and a command for safe destruction of the vehicle is sent. This procedure is unnecessary on a reusable rocket because it is equipped with a fault tolerance systemEto detect failure and return safely. The vehicle carries four engines, and if one of them fails, the remaining engines are designed to assure continued flight. Fault detection technology is also necessary. On a hydrogen rocket, a hydrogen leak could catch fire and cause a major accident. To prevent this, an onboard sensor is required to detect hydrogen. We need to build a fault tolerance system with a health management function, which can detect and locate a hydrogen leak, take the necessary measures and enable a safe return. For this system, we are developing an onboard hydrogen sensor, studying its installation position on the vehicle, as well as performing a logic study for safe return.